Process for reducing nitrogen containing compounds and lignin in tobacco

ABSTRACT

A process for reducing lignin and nitrogenous content in tobacco lamina and tobacco fiber material, including whole leaf, stems, scraps, fines and lamina, as well as burley leaf and stem, in an extraction with a solution containing hydrogen peroxide and an alkali metal hydroxide. The treated tobacco may then be further processed for use in cigarettes and other smoking articles.

BACKGROUND OF THE INVENTION

This invention relates generally to tobacco and tobacco smokingmaterials and methods of making same. More particularly, the presentinvention relates to the materials and methods that provide tobaccomaterials with reduced lignin and nitrogenous content.

Tobacco material contains various nitrogenous compounds that canadversely affect its smoke quality. Among these nitrogenous compoundsare proteins, amino acids and certain alkaloids, such as nicotine,nornicotine, anabasine and anatabine. The smoke quality of tobacco isadversely affected particularly by heterocyclic and aromatic amines, andtobacco specific nitrosamines (TSNA), as well as other compounds formedby pyrolysis or transfer of these nitrogenous compounds. Tobaccoprocessing sometimes includes steps in which the nitrogen content of thetobacco is reduced so as to improve the smokability of the tobacco.However, nitrogenous compounds are difficult to extract from curedtobacco lamina, stem, and fiber cell walls.

Many of the current processes used to reduce nitrogen content in tobaccomaterial employ enzymatic compounds and microbial agents to break downthe proteins and other nitrogen-containing compounds within the tobacco.However, disadvantages arise from the use of such enzymatic compoundsand agents. In particular, enzymes are expensive, pH sensitive anddegrade proteins into amino acids which tend to remain with the tobaccomaterial. It is also thought that enzymatic compounds leave residues ontobacco material after processing. Furthermore, microbial agents used intreating tobacco tend to cause unwanted reactions that generateundesirable by-products. Moreover, in many of these tobacco treatments,the tobacco disintegrates or easily breaks into small pieces.

Therefore, there is a need to provide a process by which the nitrogencontent of tobacco material may be reduced without leaving residues orundesirable by-products and the break-down of tobacco solid materials isreduced.

SUMMARY OF THE INVENTION

The present invention relates to a method for providing a tobaccomaterial having a reduced lignin and nitrogenous content. The tobaccomaterial in the form of flue cured and burley whole leaf lamina as wellas stems, fines, or scraps is contacted with an aqueous solvent. Theresulting liquid extract is separated from a tobacco fiber portion. Thetobacco fiber portion is then contacted with a solution containing analkali metal hydroxide, such as sodium hydroxide and/or potassiumhydroxide, and hydrogen peroxide. This solution is also separated fromthe tobacco fiber portion. The tobacco fiber portion may then be washed,refined and further processed for use in smoking articles, such ascigarettes. The reduction of lignin and nitrogenous compounds in thetobacco material provides for improved smokability and a reduction innitrogen containing pyrolitic products emitted from smoking articleswhich contain the tobacco material.

It is an object of the present invention to provide a tobacco productwith reduced levels of lignin and nitrogenous compounds.

It is another object of the present invention to provide a method ofmaking a tobacco product with reduced levels of lignin and nitrogenouscompounds.

It is a further object of the present invention to provide a method oftreating tobacco which minimizes the break-up of tobacco solidmaterials.

More particularly, the present invention is directed to a method forreducing the lignin and nitrogenous content of tobacco material,including cured tobacco whole leaf, fines, scraps, stems, and lamina, aswell as burley leaf and stem, comprising the steps of: contactingtobacco material with a first aqueous solvent, such as water, at atemperature of about 60° C. to 80° C. for about 0.5 to 1 hour;separating an aqueous tobacco extract from a tobacco fiber portion;contacting this washed tobacco fiber portion with a solution containingfrom 1% to 5% (weight/weight) alkali metal hydroxide and from 2.5% to12% (weight/weight) hydrogen peroxide at a temperature of about 25° C.to 120° C. for about 0.5 to 4 hours and, separating the resultingsolution from the tobacco fiber portion. The resulting tobacco productis then dried and used in the manufacture of cigarette articles.Alternatively, the extract, or a portion thereof, may be added back tothe tobacco product before drying.

A better understanding of the present invention will be realized fromthe hereafter processes and the Examples following such description.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic of the process steps representative of the presentinvention.

DESCRIPTION OF THE PREFERRED EMBODIMENT

In a preferred method of carrying out the lignin and nitrogen reductionprocess of the present invention, tobacco materials (10) in the form offlue cured and burley stems, scraps, fines, and/or lamina are contactedwith a first aqueous solvent (12), such as water, at a temperature ofabout 60° C. to 80° C. for about 0.5 to 1 hour. The contacting of thetobacco with the water (12) may be conducted in a tank or similar mixingvessel in which the water and tobacco are heated and agitated. Theresulting aqueous tobacco extract, containing flavor compounds, isseparated from the tobacco fiber portion, preferably by centrifugation(14). The tobacco/water slurry may be pumped into a centrifuge from themixing vessel and centrifugally separated therein. Once removed from thetobacco fiber or lamina portion, the aqueous tobacco extract (15) may bereserved for reapplication to the fiber with or without separateprocessing. In one embodiment, the aqueous tobacco extract (15) may becontacted with a solid phase adsorbent (17), such as Bentonite or acationic resin, in a vessel and then separated therefrom bycentrifugation (19), or a similar separation process well known in theart. In another embodiment, the aqueous tobacco extract (15) may bepumped or passed through specialty filters, membranes, or column packedadsorbent/absorbent materials to remove soluble nitrogenous components,such as nitrates, proteins and nitrosamines (TSBAs), and polyphenoliccompounds, and the like. The nitrogen-reduced aqueous tobacco extractcontaining flavor compounds may then be concentrated (23) by vacuumevaporation, and added back to a reconstituted tobacco paper (31).

The lignin and nitrogen content of the tobacco fiber or lamina portion(16) separated from the aqueous tobacco extract (15) may be reduced bycontacting the tobacco fiber or lamina portion (16) with a co-solventsolution containing an alkali metal hydroxide, such as sodium hydroxideand/or potassium hydroxide, and hydrogen peroxide (18). The tobaccofiber or lamina portion (16) may be loaded into a tank or similar mixingvessel. In one embodiment, a co-solvent containing from about 1.0% to5.0% (weight/weight) sodium hydroxide and 2.5% to 12.0% hydrogenperoxide (weight/weight) of tobacco fiber, preferably from 4.0% to 8.0%hydrogen peroxide, is charged to the vessel and contacted with thewashed tobacco fiber portion at a temperature of about 25° C. to 80° C.for 0.5 to 2.0 hours for lamina and from a temperature of about 70° C.to 120° C. for about 0.5 to 4.0 hours for tobacco fiber. Afterward, thesolution may be separated from the tobacco fiber or lamina portion byany means well known in the art (24), such as, for example, by pumpingthe slurry to a centrifuge wherein the fiber is centrifugally separatedfrom the solution. The tobacco fiber or lamina portion may then bewashed with a second aqueous solvent, such as water, as noted by numeral(26), and further refined (28). The tobacco fiber or lamina portion maythen be processed into sheets (30), to which may be added thelignin-nitrogen reduced aqueous tobacco extract (31). When sheets orlamina from the aforementioned process are compared to only washedsheets or lamina, there is a 35-90% reduction in Kjeldahl nitrogen and a23-45% reduction in lignin.

Additionally, potassium hydroxide (KOH) may be included in the solutionwith which the tobacco fiber portion is contacted. The tobacco fiber orlamina portion may be contacted with a solution containing potassiumhydroxide and hydrogen peroxide. The solutions set forth may containabout the same amount of potassium hydroxide as sodium hydroxide.

In particular, tobacco sheets and lamina formed from tobacco materialtreated with alkali metal hydroxide and hydrogen peroxide is strongerthan tobacco fibers and lamina processed by conventional methods. Also,this tobacco product exhibits a texture and a density that are similarto that exhibited by flue cured tobacco leaf. This tobacco product, whencut, will not crumble as easily as similar tobacco products formed byconventional methods. Therefore, less tobacco is wasted in the processof making smoking articles such as cigarettes. Thus, tobacco treated bythe above described process provides advantages in the cigarette makingprocess over conventionally treated tobacco.

EXAMPLES

For a better understanding of the present invention, the followingExamples are incorporated herein to illustrate the present inventionwith no intention of being unduly limited thereby.

Control 1 and Example 1A, 1B

A 2.8 kg mixture of tobacco materials, including flue-cured and burleytobacco scraps, stems, laminae and fines having a nitrogen content of2.09% was extracted with water at 70° C. for 30 minutes to 120 minutesas known in the art. Following centrifugation, the liquid extract wasfurther treated with adsorbent (e.g. diatomaceous clay, activatedcharcoal, clyodextrin, or combinations thereof or absorbent (celluloseacetate) to remove nitrogenous compounds, and then concentrated byvacuum evaporation. The resultant washed fiber was further extracted toremove lignin and nitrogenous compounds, as mentioned below. From thewashed fibers, 350 g portions were then loaded into vessel containing2.8-4.2 L of an alkaline-peroxide solution, comprising 2.5% (w/w) sodiumhydroxide and 7.5% (w/w) hydrogen peroxide. The alkaline-peroxidesolution containing the tobacco material was then heated to 70° C. andheld for 0.5-1 h while being agitated. After each period of heating andagitation, the liquid was separated from the tobacco fiber portionthrough centrifugation. A sample of the fibrous solids was then rinsedwith water and dried for 24 h at 35° C. The sample was then tested forlignin (Kappa number) and Kjeldahl nitrogen content and found to have alignin content of 47.145.7% and a Kjeldahl nitrogen content of0.77-0.80%, exhibiting a reduction of 23.3% to 25.5% (d.w.b) lignin anda 47.749.9% (d.w.b) Kjeldahl nitrogen from an initial Control 1 contentof 61.4% and 1.53% for lignin and Kjeldahl nitrogen, respectively, asshown in Table I. The fibrous material was then refined and formed intopaper-like sheets on a Fourdrinier type wire paper making machine.Concentrated extracts as described above were finally mixed withglycerol and added back to some of the sheets, as known in the art,before being dried at 90° C. for 3-5 minutes.

Examples 2A, 2B

These examples were carried out in a similar manner and with the samequantities of materials as in Examples 1A, 1B, except that tobaccomaterials in alkaline-peroxide solutions were heated to 90° C. and heldfor 1 h with agitation. Another exception was that one solutioncontained 4.2% (w/w) sodium hydroxide and 8.3% (w/w) hydrogen peroxide,while another contained 8.3% hydrogen peroxide only. The resulting fiberfrom the alkaline-peroxide extraction had a 30.5% reduction in ligninand a 62.8% reduction in Kjeldahl nitrogen, while the peroxide extractedfiber had a 18.6% and 20.9% reduction in lignin and Kjeldahl nitrogen,respectively.

Examples 3A, 3B

These examples were carried out in a similar manner and with the samequantities of materials as in Examples 1A, 1B, the only changes beingthat tobacco materials and solutions were heated to 120° C. and held for30 minutes. Another change was that one solution contained 2.5% sodiumhydroxide and 7.5% hydrogen peroxide, while another solution contained8.3% sodium hydroxide only. The fibrous materials from the hydroxidetreatment gave a 14.5% reduction in lignin and 85.5% reduction innitrogen, whereas the alkaline-peroxide treatment gave a 21.8% and 56.2%reduction in lignin and nitrogen content, respectively.

Control 2 and Examples 4A, 4B

A 1.9 kg batch of shredded burley stems having a Kjeldahl nitrogencontent of 2.72% was extracted with water at 70° C. for 30 minutes asknown in the art. Following centrifugation, the liquid extract waseither discarded or further treated with an adsorbent (e.g. diatomaceousclay, activated charcoal, cylodextrin, or combinations thereof) orabsorbent (cellulose acetate), or passed through a membrane/filters, toremove nitrogenous compounds, and then concentrated by vacuumevaporation. The resultant washed fiber, having a 66.4% lignin and 2.25%nitrogen content, was further extracted to remove lignin and nitrogenouscompounds, as mentioned below. From the washed fibers, 450 g portionswere then loaded into a vessel containing 2.84.2 L of analkaline-peroxide solution, comprising either of 5.0% (w/w) potassiumhydroxide (KOH) and 10.0% (w/w) hydrogen peroxide (H₂O₂) or 2.5% (w/w)KOH and 7.5% (w/w) (H₂O₂). The former alkaline-peroxide solutioncontaining the tobacco material was then heated to 90° C. and held for0.5 h, whereas the latter was heated to 120° C. and held for 0.5 h whilebeing agitated. After each period of heating and agitation, the liquidwas separated from the tobacco fiber portion through centrifugation.Each sample of the fibrous solids was then rinsed with water and driedfor 24 h at 35° C. Each sample was then tested for lignin (Kappa number)and Kjeldahl nitrogen content. When compared to the washed fiber Control2 shown in Table I, the fibrous material treated at 90° C. for 30minutes had a reduction of 45.2% for lignin and a >90% for nitrogen,while the material treated at 120° C. had a reduction of 35.8 and >90%for lignin and Kjeldahl nitrogen, respectively. Concentrated extract asdescribed above was finally mixed with glycerol and sprayed back on theshredded fibrous material in a rotating vessel chamber before beingdried at 90° C. for 5-10 minutes.

Control 3 and Examples 5A, 5B

These examples were carried out in a similar manner and with the samequantities of materials as in Examples 4A, 4B, except that shreddedflue-cure stem was substituted for shredded burley stem. The resultingfiber from the alkaline-peroxide (5.0 vs. 10.0%) extraction at 90° C.for 0.5 h had a reduction of 43.1% lignin and a >88.8% nitrogen whencompared to control 3 values, shown in Table I. The resulting fiber fromthe alkaline peroxide (2.5 vs. 7.5%) extraction at 120° C. for 0.5 h hada reduction of 38.6% lignin and >88.8% nitrogen when compared to Control3 values, shown in Table I.

Control 4 and Examples 6A, 6B

These examples were carried out in the same manner as in Example 4 andwith the same quantities of materials as in Examples 1A, 1B, the onlychanges being that a mixture of flue-cure and burley laminae (17-22 cutsper inch²) was the staring material. Other changes included heatingvessel contents to 90° C. for 0.5 h, and using alkaline-peroxidesolutions containing either 3.5% NaOH and 6.0% H₂O₂ or 6.0% NaOH and11.5% H₂O₂. Resulting fiber from the alkaline-peroxide (3.5 vs. 6.0%)extraction at 90° C. for 0.5 h had a reduction of 36.6% lignin and 59.7%nitrogen when compared to Control 4 values, shown in Table I. Theresulting fiber from the alkaline-peroxide (6.0 vs. 11.5%) extraction at90° C. fro 0.5 h had a reduction of 43.5% lignin and 69.8% nitrogen whencompared to Control 4 values, shown in Table I.

Control 5 and Examples 7A, 7B

These examples were carried out in the same manner as in Examples 4A,4B, and with the same quantities of materials as in Examples 1A, 1B, theonly changes being that burley lamina (17-22 cuts per inch²) was thestaring material. Another change was holding extraction vessel contentsat 25° C. for 2 h, and using alkaline-peroxide solution containing 1.25%NaOH and 3.75% H₂O₂ or heating vessel contents to 70° C. and holding 0.5h, and using 2.5% NaOH and 7.5% H₂O₂. Resulting fiber from thealkaline-peroxide (1.25 vs. 3.75%) extraction at 25° C. for 2 h had areduction of 14.5% lignin and 49.9% nitrogen when compared to Control 5values, shown in Table I. The resulting fiber from the alkaline-peroxide(2.5 vs. 7.5%) extraction at 70° C. for 0.5 h had a reduction of 29.2%lignin and 63.5% nitrogen when compared to Control 5 values, shown inTable I.

Control 6 and Examples 8A, 8B

These examples were carried out in the same manner and same quantitiesas in Examples 7A, 7B, the only changes being that flue-cure lamina(17-22 cuts per inch²) was the staring material. Resulting fiber fromthe alkaline-peroxide (1.25 vs. 3.75%) extraction at 25° C. for 2 h hada reduction of 16.6% lignin and 50.4% nitrogen when compared to Control6 values, shown in Table I. The resulting fiber from thealkaline-peroxide (2.5 v. 7.5%) extraction at 70° C. for 0.5 h had areduction of 28.8% lignin and 43.0% nitrogen when compared to Control 6values, shown in Table I. TABLE I Reductions in Kjeldahl nitrogen andlignin of tobacco extracted with alkaline-peroxide solutions % (w/w)solution Extraction (dry weight basis) % Kjeldahl Temp. Temp. AlkaliPeroxide nitrogen % Nitrogen % Lignin % Lignin Starting material (° C.)(min) (NaOH or KOH) (H₂O₂) (dwb) reduction (Kappa number) reductionMixed tobacco materials Control 1 70 30 — — 1.53 — 61.4 — Aqueously (ag)extracted material (AE) 1A 70 30 2.5 7.5 0.80 47.7 47.1 23.3 1B 70 120 2.5 7.5 0.77 49.7 45.7 25.5 2A 90 60 — 8.3 1.21 20.9 50.2 18.6 2B 90 604.2 8.3 0.48 62.8 42.7 30.5 3A 120  30 2.5 7.5 0.87 56.2 48.0 21.8 3B120  30 8.3 — 0.22 85.6 52.5 14.5 Shredded Stems Control 2 70 30 — —2.25 — 66.4 — Aq. Extracted burley (RAE) 4A 80 30 5.0 10.0  Bcl* (0.22)90.2 36.4 45.2 4B 120  30 2.5 7.5 Bcl (0.22) 90.2 42.6 35.8 Control 3 7030 — — 1.98 — 60.6 — Aq Extracted flue-cure (FAE) 5A 90 30 5.0 10.0  Bcl(0.22) 88.8 34.5 43.1 58 120  30 2.5 7.5 Bcl (0.22) 88.8 37.2 38.8Control 4 70 30 — — 2.92 — 61.5 — Aq Extracted mixed flue-cure/ burley(LAE) 6A 90 30 3.5 6.0 1.18 59.6 39.2 30.6 6B 90 30 6.0 11.5  0.88 69.834.7 43.5 Control 5 70 30 — — 3.95 — 62.3 — Aq Extracted burley (BLAE)7A 25 120   1.25  3.75 1.98 49.9 53.3 14.5 7B 70 30 2.6 7.6 1.47 83.544.1 29.2 Control 6 70 30 — — 2.67 — 60.4 — Aq Extracted flue-cure(FLAE) 8A 25 120   1.25  3.75 1.45 43.8 50.4 16.6 8B 70 30 2.5 7.5 1.1356.0 43.0 28.8*BELOW CALIBRATION LIMITFrom the Examples it is seen that a significant reduction of both ligninand nitrogen is obtained by contacting tobacco with a mixture of alkalimetal hydroxide and hydrogen peroxide from 1% to 5% by weight in asolution and the hydrogen peroxide is from 2.5% to 12%.

The foregoing detailed description and Examples are given primarily forclearness of understanding and no unnecessary limitations are to beunderstood therefrom for modifications will become obvious to thoseskilled in the art upon reading the disclosure and may be made withoutdeparting from the spirit of the invention and scope of the appendedclaims.

1. A method of making a tobacco material with reduced levels of ligninand nitrogenous compounds comprising: (a) contacting a tobacco materialwith a first aqueous solvent at a temperature of about 25° C. to 80° C.for about 0.5 to 2 hours to provide an aqueous tobacco extract and atobacco fiber portion; (b) separating said aqueous tobacco extract fromsaid tobacco fiber portion; (c) contacting at a temperature from about25° C. to 120° C. said tobacco fiber portion with a solution containinghydrogen peroxide and an alkali metal hydroxide wherein said solutioncontains said hydrogen peroxide in a concentration of from 2.5% to 12.0%(w/w) and said alkali metal hydroxide is from about 1% to 5% (w/w); and,(d) separating said solution from said tobacco fiber portion.
 2. Themethod of claim 1, further comprising: (e) contacting said tobacco fiberportion with a second aqueous solvent.
 3. The method of claim 1, whereinsaid tobacco material is lamina.
 5. The method of claim 1, wherein saidalkali metal hydroxide is sodium hydroxide.
 6. The method of claim 5,wherein said sodium hydroxide is from about 4% to 8 (w/w).
 7. The methodof claim 5, wherein said alkali metal hydroxide is potassium hydroxide.8. The method of claim 7, wherein said potassium hydroxide is from about4% to 8% (w/w).